The vasodilator 17,18-epoxyeicosatetraenoic acid targets the pore-forming BK [alpha] channel subunit in rodents

• Published in: Experimental physiology Vol. 92; no. 6; p. 1067
• Main Authors: Hercule, Hantz C, Salanova, Birgit, Essin, Kirill, Honeck, Horst, Falck, John R, Sausbier, Matthias, Ruth, Peter, Schunck, Wolf-Hagen, Luft, Friedrich C, Gollasch, Maik
• Format: Journal Article
• Language: English
• Published: Oxford John Wiley & Sons, Inc 01.11.2007
• ISSN: 0958-0670; 1469-445X
• DOI: 10.1113/expphysiol.2007.038166

17,18-Epoxyeicosatetraenoic acid (17,18-EETeTr) stimulates vascular large-conductance K+(BK) channels. BK channels are composed of the pore-forming BK α and auxiliary BK β1 subunits that confer an increased sensitivity for changes in membrane potential and calcium to BK channels. Ryanodine-sensitive calcium-release channels (RyR3) in the sarcoplasmic reticulum (SR) control the process. To elucidate the mechanism of BK channel activation, we performed whole-cell and perforated-patch clamp experiments in freshly isolated cerebral and mesenteric artery vascular smooth muscle cells (VSMC) from Sprague-Dawley rats, BK β1 gene-deficient (-/-), BK α (-/-), RyR3 (-/-) and wild-type mice. The 17,18-EETeTr (100 nm) increased tetraethylammonium (1 mm)-sensitive outward K+currents in VSMC from wild-type rats and wild-type mice. The effects were not inhibited by the epoxyeicosatrienoic acid (EET) antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (10 μm). BK channel currents were increased 3.5-fold in VSMC from BK β1 (-/-) mice, whereas a 2.9-fold stimulation was observed in VSMC from RyR3 (-/-) mice (at membrane voltage 60 mV). The effects were similar compared with those observed in cells from wild-type mice. The BK current increase was neither influenced by strong internal calcium buffering (Ca2+, 100 nm), nor by external calcium influx. The 17,18-EETeTr did not induce outward currents in VSMC BK α (-/-) cells. We next tested the vasodilator effects of 17,18-EETeTr on isolated arteries of BK α-deficient mice. Vasodilatation was largely inhibited in cerebral and mesenteric arteries isolated from BK α (-/-) mice compared with that observed in wild-type and BK β1 (-/-) arteries. We conclude that 17,18-EETeTr represents an endogenous BK channel agonist and vasodilator. Since 17,18-EETeTr is active in small arteries lacking BK β1, the data further suggest that BK α represents the molecular target for the principal action of 17,18-EETeTr. Finally, the action of 17,18-EETeTr is not mediated by changes of the internal global calcium concentration or local SR calcium release events.